Dynamics of death by heat.

It has been known for a century that mortality from heat depends not only on the exposure temperature but also on the duration of exposure (1). Typically, higher temperature shortens time to death. But predicting heat death in nature is challenging because an animal's temperature and stress level—especially for small species—can fluctuate markedly within days and across seasons. Can risk of heat death in fluctuating environments be understood only by brute-force experiments involving all possible temperature sequences, or can exposure to a few fixed temperatures capture key dynamics of heat death? On page 1242 of this issue, Rezende et al. (2) extend a recently developed mathematical model (3) and show that fixed-temperature experiments can be generalized to dynamic patterns and can predict mortality of a fly (Drosophila subobscura) in nature across seasons and climate shifts.